Title Control of Neutrophil Effector Mechanisms by the IRE1-Caspase2 signaling axis Project Summary/Abstract Neutrophils are a key component of defense against methicillin-resistant Staphylococcus aureus (MRSA) infection, the leading cause of hospital-acquired infection worldwide. Increasing antibiotic resistance in this pathogen highlights a compelling need to identify pathways for developing new therapeutics to treat MRSA infections. We recently showed that the endoplasmic reticulum (ER) stress sensor, IRE1?, amplifies macrophage innate immune defenses against MRSA, and in a murine abscess model of infection. In macrophages, the IRE1?-CASPASE-2 signaling axis was a potent regulator of IL-1? production, essential for resolving MRSA infection in vivo. Neutrophils also play a critical role in clearing MRSA infection, but the role of IRE1? and CASPASE-2 in governing neutrophil function is largely unknown. Our preliminary data reveal a strong requirement for IRE1? and CASPASE-2 in regulating murine and human neutrophil effector functions, pointing to a current gap in our understanding of how ER stress responses control neutrophil-mediated host immunity. Thus, the objective of this proposal is to elucidate the mechanisms by which the neutrophil ER stress response controls innate immune effector function. We hypothesize that infection triggers IRE1?-CASPASE-2 signaling, which enhances IL-1? production, and promotes NET formation. This hypothesis will be tested by: 1) defining the mechanistic contribution of IRE1?-CASPASE-2 signaling to neutrophil IL-1? production during MRSA infection, and 2) elucidating the role of IRE1?-CASPASE-2 signaling in NET formation. The contribution of this signaling pathway to NET formation under conditions relevant to autoimmune disease will also be tested, since NETs have been implicated in the development of autoimmune syndromes, like lupus. The knowledge gained from completion of this study will establish the ER stress response as an important regulatory network in neutrophil effector function, and will lay the groundwork for developing therapies that may prove useful in modulating inflammation acutely during infection by antibiotic-resistant pathogens or chronically in autoimmune diseases.